Tele Vue Ethos 21 mm Eyepiece

"Ethos 21mm: Maximize your "spacewalk"

Maximize your "spacewalk" experience with the 21mm Ethos. Transform your passage through the Milky Way with the 21mm’s nexus of contrast, power and field. Larger deep sky objects and rich star fields are its natural playground. Looking on-axis your field-of-vision is filled with 100º of stars, however wherever you chose to concentrate your attention you’ll see sharpness and richer contrast.

Extending the Ethos focal length range to 21mm while maintaining the original performance goals of the rest of the series brings the eyepiece up against the mechanical limits of the 2” barrel and focus constraints. The 21mm provides the maximum true field of view, has no significant vignetting at the edge of the field, and is parfocal with the 31mm Nagler Type 5.

The 21mm focal length completes the logical set of 21mm/13mm/8mm and nicely juxtaposes the 17mm/10mm/6mm combination. Each step within these two sets approaches a 3X field area gain. The 21mm’s effective field stop diameter is 36.2mm, bringing its true field close to the 35mm Panoptic (38.7mm Field Stop diameter). Its true field is also larger than the 26mm Nagler with its 35mm effective field stop diameter. In an f/4 Dobsonian, the exit pupil is just 5.25mm using the 21mm Ethos instead of 8.75mm with a 35mm Panoptic, or 6.5mm with a 26mm Nagler.

Excerpts from Ethos 21mm Review in SkyNews! Todd Carlson: "More 100-Degree-Eyepiece Choices". SkyNews, (Jan/Feb 2010).

The massive Tele Vue 21mm Ethos eyepiece is the longest focal length available in the company's 100-degree-field-of-view eyepiece series. The Ethos line is setting the standard for high-end eyepieces. As with all other focal lengths in the Ethos line, the 21mm has a comfortable 15mm of eye relief. And, not surprisingly, this new eyepiece performs as exceptionally as do its Ethos siblings. In my 12.5-inch f/4.8 PortaBall reflector, the 21mm Ethos provides a magnification of 72x and a stunning 1.4-degree field of view. I enjoyed the best view of M31 that I've ever seen though this telescope, with tight stars at the edge of the field. And the wispy tentacles of the Orion Nebula extend almost to the edge of the field of view, affording a unique and detailed view of the nebula. The 21mm Ethos in the 11-inch SCT provides a 0.74-degree field of view at 133x, a magnification I prefer for many deep-sky objects. My observing partner and I enjoyed beautiful views of the Perseus Double Cluster, an open star cluster that, in my opinion, loses its beauty when observed through the SCT's typical narrow field of view. When the 21mm Ethos was used in a Tele Vue 76 refractor, the resulting magnification of 25x and the humongous four-degree field of view provided an outstanding view of the Pleiades star cluster floating in a star-rich field. While the 21mm Ethos excelled in the short-focal-length refractor, it was most impressive when used with the SCT — so much so that I'm going to christen this focal length the "SCT-Ethos." SCT owners are no longer restricted to relatively low magnification to enjoy a comfortable field of view. This latest member of the respected Ethos family fits the tradition set by previous five.

Reviewers Ratings of the Ethos Eyepiece

BBC Sky at Night Magazine
Build Quality	98%
Ease of Use	95%
Field of View	100%
Optical Quality	98%
Value for Money	90%
Overall	96%
Sky & Telescope
Optical Performance	* * * * *
Sensibly perfect. No meaningful improvements possible.

Tele Vue 21mm Ethos Specifications

• Apparent Field: 100°
• Focal Length: 21mm
• Effective Field Stop: 36.2mm
• Eye Relief: 15mm (accepts DIOPTRX™ eyesight astigmatism corrector)
• Barrel Size: 2"
• Weight: 2.25lbs.

Now you can have your own 21mm Tele Vue Ethos Eyepiece from Venturescope for £689.00!